1、都知道SpringMVC项目启动的时候都会初始化一个类：DispatcherServlet,看这个类的源码我们可以发现他其实就是一个servlet，
为什么这么说呢？请看：
DispatcherServlet extends FrameworkServlet
FrameworkServlet extends HttpServletBean
HttpServletBean extends HttpServlet
初始化这个DispatcherServlet的时候我们可以看到这个类里面有一个静态代码块：根据代码可以看出代码块里面会去读取DispatcherServlet.properties配置文件里面的配置，load到Properties集合里面
private static final String DEFAULT_STRATEGIES_PATH = "DispatcherServlet.properties";
private static final Properties defaultStrategies;
static {
try {
ClassPathResource resource = new ClassPathResource(DEFAULT_STRATEGIES_PATH, DispatcherServlet.class);
defaultStrategies = PropertiesLoaderUtils.loadProperties(resource);
}
catch (IOException ex) {
throw new IllegalStateException("Could not load '" + DEFAULT_STRATEGIES_PATH + "': " + ex.getMessage());
}
}
2、我们都知道一个servlet初始化阶段 ，会调用init()方法，那么这边会先调用HttpServlet的子类HttpServletBean里面的init方法：org.springframework.web.servlet.HttpServletBean#init，这个方法里面调用了initServletBean这个方法：org.springframework.web.servlet.FrameworkServlet#initServletBean
@Override
public final void init() throws ServletException {
if (logger.isDebugEnabled()) {
logger.debug("Initializing servlet '" + getServletName() + "'");
} // Set bean properties from init parameters.
PropertyValues pvs = new ServletConfigPropertyValues(getServletConfig(), this.requiredProperties);
if (!pvs.isEmpty()) {
try {
BeanWrapper bw = PropertyAccessorFactory.forBeanPropertyAccess(this);
ResourceLoader resourceLoader = new ServletContextResourceLoader(getServletContext());
bw.registerCustomEditor(Resource.class, new ResourceEditor(resourceLoader, getEnvironment()));
initBeanWrapper(bw);
bw.setPropertyValues(pvs, true);
}
catch (BeansException ex) {
if (logger.isErrorEnabled()) {
logger.error("Failed to set bean properties on servlet '" + getServletName() + "'", ex);
}
throw ex;
}
} // Let subclasses do whatever initialization they like.
initServletBean(); if (logger.isDebugEnabled()) {
logger.debug("Servlet '" + getServletName() + "' configured successfully");
}
}
org.springframework.web.servlet.FrameworkServlet#initServletBean里面调用了org.springframework.web.servlet.FrameworkServlet#initWebApplicationContext
@Override
protected final void initServletBean() throws ServletException {
getServletContext().log("Initializing Spring FrameworkServlet '" + getServletName() + "'");
if (this.logger.isInfoEnabled()) {
this.logger.info("FrameworkServlet '" + getServletName() + "': initialization started");
}
long startTime = System.currentTimeMillis(); try {
this.webApplicationContext = initWebApplicationContext();
initFrameworkServlet();
}
catch (ServletException | RuntimeException ex) {
this.logger.error("Context initialization failed", ex);
throw ex;
} if (this.logger.isInfoEnabled()) {
long elapsedTime = System.currentTimeMillis() - startTime;
this.logger.info("FrameworkServlet '" + getServletName() + "': initialization completed in " +
elapsedTime + " ms");
}
}
org.springframework.web.servlet.FrameworkServlet#initWebApplicationContext
protected WebApplicationContext initWebApplicationContext() {
WebApplicationContext rootContext =
WebApplicationContextUtils.getWebApplicationContext(getServletContext());
WebApplicationContext wac = null;
if (this.webApplicationContext != null) {
// A context instance was injected at construction time -> use it
wac = this.webApplicationContext;
if (wac instanceof ConfigurableWebApplicationContext) {
ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) wac;
if (!cwac.isActive()) {
// The context has not yet been refreshed -> provide services such as
// setting the parent context, setting the application context id, etc
if (cwac.getParent() == null) {
// The context instance was injected without an explicit parent -> set
// the root application context (if any; may be null) as the parent
cwac.setParent(rootContext);
}
configureAndRefreshWebApplicationContext(cwac);
}
}
}
if (wac == null) {
// No context instance was injected at construction time -> see if one
// has been registered in the servlet context. If one exists, it is assumed
// that the parent context (if any) has already been set and that the
// user has performed any initialization such as setting the context id
wac = findWebApplicationContext();
}
if (wac == null) {
// No context instance is defined for this servlet -> create a local one
wac = createWebApplicationContext(rootContext);
}
if (!this.refreshEventReceived) {
// Either the context is not a ConfigurableApplicationContext with refresh
// support or the context injected at construction time had already been
// refreshed -> trigger initial onRefresh manually here.
onRefresh(wac);
}
if (this.publishContext) {
// Publish the context as a servlet context attribute.
String attrName = getServletContextAttributeName();
getServletContext().setAttribute(attrName, wac);
if (this.logger.isDebugEnabled()) {
this.logger.debug("Published WebApplicationContext of servlet '" + getServletName() +
"' as ServletContext attribute with name [" + attrName + "]");
}
}
return wac;
}里面有一个onRefresh方法：里面做了一些列的初始化操作，具体哪个方法对应什么功能呢？请大家自行看里面的源码，我这边主要说的是
initHandlerMappings(context);
initHandlerAdapters(context);
这两个方法就是初始化我们的映射器和我们的适配器的，到此我们的初始化就结束了；
@Override
protected void onRefresh(ApplicationContext context) {
initStrategies(context);
} protected void initStrategies(ApplicationContext context) {
//此方法主要做文件上传处理的
initMultipartResolver(context);
initLocaleResolver(context);
initThemeResolver(context);
//此方法主要是获取配置文件DispatcherServlet.properties里面的handlerMapping类型对象
initHandlerMappings(context);
initHandlerAdapters(context);
initHandlerExceptionResolvers(context);
initRequestToViewNameTranslator(context);
initViewResolvers(context);
initFlashMapManager(context);
}